One source, many subscribers in RxJS
RxJS interview exercise on Subjects & sharing, difficulty 3 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write shared(source$): subscribers share one subscription to the source while at least one is listening, and a new subscription to the source is made when subscribers return after all had left. Also cached(source$): like shared, but a late subscriber also gets the latest value, and the source is never subscribed a second time.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.